Reconciliation of the Carrying Amounts of Shareholders' Equity (Parenthetical) (Detail) (USD $)	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Stockholders Equity Note [Line Items]
Dividends paid, per share	$ 0.16875	$ 0.16875

Aggregate dividends paid during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

Name:	us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix:	us-gaap
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration